1. Field of the Invention
The present invention is directed in general to the field of information processing. In one aspect, the present invention relates to a system and method for managing automatic retransmission request signals in communication networks.
2. Description of the Related Art
Wireless communication systems transmit and receive signals within a designated electromagnetic frequency spectrum, but capacity of the electromagnetic frequency spectrum is limited. As the demand for wireless communication systems continues to expand, there are increasing challenges to improve spectrum usage efficiency. To improve the communication capacity of the systems while reducing the sensitivity of the systems to noise and interference and limiting the power of the transmissions, a number of wireless communication techniques have been proposed, such as Multiple Input Multiple Output (MIMO), which is a transmission method involving multiple transmit antennas and multiple receive antennas. Such wireless communication systems are increasingly used to distribute or “broadcast” audio and/or video signals (programs) to a number of recipients (“listeners” or “viewers”) that belong to a large group. An example of such a wireless system is the 3GPP LTE (Long Term Evolution) system depicted in FIG. 1, which schematically illustrates the architecture of an LTE wireless communication system 100. As depicted, the broadcast server 102 communicates through an EPC 104 (Evolved Packet Core) which is connected to one or more access gateways (AGW) 106, 108 that control transceiver devices, 110, 112, 114, 116 which communicate with the end user devices 118, 120, 122, 124, 126, 128. In the LTE architecture, the transceiver devices 110, 112, 114, 116 may be implemented with base transceiver stations (referred to as enhanced Node-B or eNB devices) which in turn are coupled to Radio Network Controllers or access gateway (AGW) devices 106, 108 which make up the UMTS radio access network (collectively referred to as the UMTS Terrestrial Radio Access Network (UTRAN)). Each transceiver device 110, 112, 114, 116 includes transmit and receive circuitry that is used to communicate directly with any mobile end user(s) 118, 120, 122, 124, 126, 128 located in each transceiver device's respective cell region. Thus, transceiver device 110 includes a cell region 120 having one or more sectors in which one or more mobile end users 124, 126 are located. Similarly, transceiver device 112 includes a cell region 132 having one or more sectors in which one or more mobile end users 128 are located, transceiver device 114 includes a cell region 134 having one or more sectors in which one or more mobile end users 118, 120 are located, and transceiver device 116 includes a cell region 136 having one or more sectors in which one or more mobile end users 122 are located. With the LTE architecture, the eNBs 110, 112, 114, 116 are connected by an S1 interface to the EPC 104, where the S1 interface supports a many-to-many relation between AG Ws 106, 108 and the eNBs 110, 112, 114, 116.
As will be appreciated, each transceiver device, e.g., eNB 110, in the wireless communication system 100 includes a transmit antenna array and communicates with receiver device, e.g., user equipment (UE) 128, having a receive antenna array, where each antenna array includes one or more antennas. The wireless communication system 100 may be any type of wireless communication system, including but not limited to a MIMO system, SDMA system, CDMA system, SC-FDMA system, OFDMA system, OFDM system, etc. Of course, the receiver/subscriber stations, e.g., UE 128, can also transmit signals which are received by the transmitter/base station, e.g., eNB 112. The signals communicated between transmitter 112 and user device 128 can include voice, data, electronic mail, video, and other data, voice, and video signals.
Various transmission strategies require the transmitter to have some level of knowledge concerning the channel response between the transmitter and each receiver, and are often referred to as “closed-loop” systems. An example application of closed-loop systems which exploit channel-side information at the transmitter (“CSIT”) are precoding systems, such as space division multiple access (SDMA), which use closed-loop systems to improve spectrum usage efficiency by applying precoding at the transmitter to take into account the transmission channel characteristics, thereby improving data rates and link reliability. SDMA based methods have been adopted in several current emerging standards such as IEEE 802.16 and the 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) platform. With such precoding systems, CSIT can be used with a variety of communication techniques to operate on the transmit signal before transmitting from the transmit antenna array. For example, precoding techniques can provide a multi-mode beamformer function to optimally match the input signal on one side to the channel on the other side. In situations where channel conditions can be provided to the transmitter, closed loop methods, such as MIMO precoding, can be used. Precoding techniques may be used to decouple the transmit signal into orthogonal spatial stream/beams, and additionally may be used to send more power along the beams where the channel is strong, but less or no power along the weak, thus enhancing system performance by improving data rates and link reliability. In addition to multi-stream transmission and power allocation techniques, adaptive modulation and coding (AMC) techniques can use CSIT to operate on the transmit signal before transmission on the transmit array.
With conventional closed-loop MIMO systems, full broadband channel knowledge at the transmitter may be obtained by using uplink sounding techniques (e.g., with Time Division Duplexing (TDD) systems). Alternatively, channel feedback techniques can be used with MIMO systems (e.g., with TDD or Frequency Division Duplexing (FDD) systems) to feed back channel information to the transmitter.
It will be appreciated that for simplicity and clarity of illustration, elements illustrated in the drawings have not necessarily been drawn to scale. For example, the dimensions of some of the elements are exaggerated relative to other elements for purposes of promoting and improving clarity and understanding. Further, where considered appropriate, reference numerals have been repeated among the drawings to represent corresponding or analogous elements.